: During the previous three years, the investigators demonstrated that kappa opioid receptor stimulation or muscarinic receptor stimulation decreases dialysate glutamate levels in the dorsal striatum evoked by L-trans-PDC. They established that local perfusion of the kappa agonist, U-69593 completely blocked an amphetamine-induced increase in dialysate glutamate levels and significantly decreased amphetamine-induced dialysate dopamine levels in the nucleus accumbens. The ability of amphetamine to increase dopamine and glutamate levels was partially calcium-dependent and the effect of U-69593 was totally calcium-dependent. These investigators observed similar calcium-dependent effects of amphetamine in the dorsal striatum challenging the dogma that amphetamine-induced dopamine release is exclusively calcium-dependent in vivo. The studies proposed herein will extend these findings to other metabotropic systems implicated in the modulation of dopamine-glutamate interactions in the dorsal and ventral striatum. Furthermore, in order to prove or disprove a presynaptic mechanism of action of glutamate regulators, isolated nerve terminals, or synaptosomes, will be used in addition to microdialysis in the following specific aims. 1. The mechanism of action of amphetamine-induced dialysate glutamate levels in the dorsal and ventral striatum of awake rats will be investigated by in vivo microdialysis coupled with HPLC analysis. 2. The ability of selected metabotropic receptors (opioid, muscarinic, glutamate, and GABA-B) to regulate dialysate glutamate levels by acute administration of psychostimulants will be investigated by in vivo microdialysis/HPLC. 3. The ability of these metabotropic receptors to regulate striatal glutamate levels evoked by repeated administration of psychostimulants in sensitized rats will be determined by in vivo microdialysis/HPLC. 4. The ability of the metabotropic receptors studied in vivo to presynaptically inhibit evoked glutamate efflux in striatal synaptosomes will be determined by spectrofluorometric analysis. These studies should contribute to the understanding of transsynaptic and direct presynaptic regulation of striatal glutamate efflux in response to psychostimulants. This research is intended to target novel neurotransmitter systems for medicinal development with the goal of treating the widespread abuse of cocaine and amphetamines.